As to a speech discrimination used as preprocessing of a speech recognition, it is required that a user's speech is correctly detected from various disturbance sounds such as a road-noise of an automobile or a system sound (For example, a beep sound, a guidance speech) uttered by a system. For example, as a speech discrimination method that robustness for the system sound is raised, by specifying a frequency band including a main power of the system sound, when a feature is extracted from an acoustic signal, a frequency spectrum of the frequency band is excluded. By this method, the feature excluding an influence of the disturbance sound (system sound) can be extracted.
However, in this method, when a frequency band to be excluded is determined, a frequency spectrum of the system sound is only used. Accordingly, if a main element of a user's speech is included in the same frequency band as the system sound, when the frequency band including a main element of the system sound is excluded, the main element of the user's speech is also excluded. As a result, an accuracy to discriminate speech/non-speech falls.